Radio-frequency (RF) switches are used in a multiplicity of RF circuits in order to implement different functions. Resonant circuits can be set for resonance operation for example by means of an RF switch. Such resonant circuits can be used for example as antennas in mobile communication devices.
In detail, for example, a communication system that uses different frequencies for different signalling methods can be implemented using a network of RF switches. The RF switches can be used to select between different types of RF front-end circuits. One example of such a communication system is a multi-standard mobile telephone that can carry out telephone calls using different standards, such as, for example, Third Generation Partnership Project (3GPP) Code Division Multiple Access (CDMA) or 3GPP Global System for Mobile Communications (GSM) or 3GPP Long Term Evolution (LTE). One and the same communication standard, moreover, can use different frequencies e.g. depending on the network operator. Using an RF switch, an RF front-end circuit optimized for CDMA communication can be used for CDMA telephone calls; while an RF front-end circuit optimized for GSM communication can be used for GSM telephone calls.
Furthermore, RF switches can be used to implement settable matching networks for antennas or power amplifiers. In this way it is possible to provide settable adjustment of RF filters by connection and disconnection and/or bypassing of passive matching and setting elements.
In order to provide RF switches having a particularly high dielectric strength, techniques are known which use a stack comprising field effect transistors (FETs) coupled in series. Typical dielectric strengths for switches are e.g. in the region of 24 V for 50-ohm mobile radio applications and up to 100 V on antenna resonant circuits for an open state of the switch. Since the individual components of typical production techniques such as, for example, the complementary metal oxide semiconductor (CMOS) process are not designed for such high voltages, the stacked arrangement of a multiplicity of FETs is used. The voltage can then be distributed among the multiplicity of FETs, such that each individual FET is exposed only to a lower voltage. By way of example, individual FETs in a CMOS silicon-on-insulator (SOI) process typically have a maximum dielectric strength between source contact and drain contact of 2.5 V. 40 FETs, for example, are then stacked in order to obtain the dielectric strength of 100 V; see U.S. Pat. No. 4,317,055, for example, for corresponding techniques.
However, such RF switches have certain disadvantages and/or limitations. By way of example, it may be possible that a lower limiting frequency for the voltage change at the input terminal exists for a specific dimensioning of the components used; see Shifrin, Mitchell B., Peter J. Katzin, and Yalcin Ayasli. “Monolithic FET structures for high-power control component applications.” IEEE Trans. Microwave Theory and Techniques, 37 (1989) 2134-2141; equations 12, 14 and 15. If the voltage at the input terminal varies with a frequency that is lower than said limiting frequency, damage to the FETs used can occur. The switch can thus become unusable.
A slow variation of the voltages over time can often occur in association with electrostatic discharge (ESD).
U.S. Pat. No. 8,461,903 B1 discloses techniques in which comparatively fast switchover times can be achieved despite a conservative dimensioning of the components used—and thus an improved robustness vis à vis ESD events. However, a corresponding switch can be comparatively complicated and costly in terms of production. Moreover, a corresponding switch typically requires a PMOS transistor; however, a corresponding transistor is not available in various production techniques, with the result that such techniques cannot be usable or can be usable only to a limited extent.